8-71
8-114E The work produced for the process 1-2 shown in the figure is to be determined.
Assumptions Kinetic and potential energy changes are negligible.
Analysis The work integral represents the area to the
left of the reversible process line. Then,
P (psia)
2
win,1- 2
2
500
³ vdP
1
v1 v 2
2
( P2 P1 )
100
§
(0.1 1.7)ft 3 /lbm
1 Btu
(500 100)psia ¨
3
¨
2
© 5.404 psia ˜ ft
·
¸
¸
¹
1
0.1
v (ft3/lbm)
1.7
66.6 Btu/lbm
8-115 Liquid water is to be pumped by a 25-kW pump at a specified rate. The highest pressure the water
can be pumped to is to be determined.
Assumptions 1 Liquid water is an incompressible substance. 2 Kinetic and potential energy changes are
negligible. 3 The process is assumed to be reversible since we will determine the limiting case.
Properties The specific volume of liquid water is given to be v1 = 0.001 m3/kg.
Analysis The highest pressure the liquid can have at the pump exit can be determined from the reversible
steady-flow work relation for a liquid,
Win
§
m ¨
©
³
2
1
·
vdP 'ke©0 'pe©0 ¸
¹
m v1 P2 P1 P2
Thus,
25 kJ/s
§ 1 kJ ·
¸
(5 kg/s)(0.001 m3/kg )( P2 100) k Pa ¨¨
3¸
© 1 kPa ˜ m ¹
25 kW
PUMP
It yields
P2
5100 kPa
100 kPa
PROPRIETARY MATERIAL. © 2008 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and
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